A new survey puts Colorado second-highest in the nation for parents refusing vaccines for their school-age kids, part of an anti-shot trend that increasingly troubles state health officials.

Though some public-health officials said the Associated Press ranking exaggerates the vaccine-refusal rates in Colorado, most said there is worrisome sentiment building against immunization. They said Colorado’s education system makes it too easy to opt out of shots and that a highly educated population employs bad information to reject vaccines.

Parents still cite a fraudulent autism study when refusing shots in Colorado and other states, said Dr. Simon Hambidge, director of general pediatrics at Denver Health Medical Center.

“The number of people exposed to measles, mumps and other viruses because of that deception is truly astounding,” Hambidge said.

A public-health ranking last year said Colorado’s status had dropped because vaccine rates for the youngest children had slipped from 92 percent to 85 percent.

“The data is not perfect, either for Colorado or the nation. However, it does appear there is a slow but steady increase in the number of parents who either refuse vaccines or defer them,” said Dr. Matt Daley, a Kaiser Permanente pediatrician who also researches vaccine rates.

Expert opinions are clear, despite growing public questions: The dangers of a disease are far greater than the minimal risk of side effects from a vaccine. And, Daley said, kids who are not vaccinated are 23 times more likely to get whooping cough, for example, than those who are immunized.

The AP survey of states said 7 percent of Colorado kindergarten students took exemptions from required immunizations in 2010-11. Alaska had the highest exemption rate, at nearly 9 percent, the AP said.

Minnesota’s was 6.5 percent, with Vermont and Washington at 6 percent. Oregon, Michigan and Illinois were close behind. Mississippi had the lowest exemption rate at essentially 0 percent.

Colorado’s director of public-health programs, Joni Reynolds, said state surveys show only a 6.3 percent exemption rate among kindergartners last year. That is not significantly different from 6.1 percent in 2004-05, she said, though state figures dipped to 4.6 percent in 2005-06.

The Associated Press also used federal surveys that sometimes differ from state tallies.

Other public-health experts said more parents are questioning vaccines and that Colorado makes it too simple to opt out.

The state is one of about 20 that allows parents to opt out merely because they have objections to vaccines. Some return a signed exemption form even if their children are vaccinated because it’s easier than finding proof of inoculations, officials said.

Renee Chalfant of Boulder refused many vaccinations for her children, now grown, and would do it again. She said she has read hundreds of studies and is convinced it’s better for children to be exposed to disease and develop natural immunity if they live in a nation where health care is available.

“I made a concerted effort to expose my children to every disease I could find, from chicken pox to strep to whooping cough. They were exposed purposefully and with a plan,” she said.

Other parents who hear of the refusal rates are appalled.

“Any parent that chooses to not vaccinate their children is putting all other children at risk,” said Christa Wilson of Denver.

Receding vaccine rates open the way for long-quelled diseases to return in Colorado, such as a whooping-cough outbreak last year. Whooping cough killed 10 in California in 2010. Measles threats also surfaced in other nations.

“If you start getting (vaccination rates) below certain levels, a measles outbreak is only a plane flight away,” said Dr. Ned Calonge, president of the Colorado Trust and former public-health director for the state.

Michael Booth was a health care & health policy writer at The Denver Post before departing in 2013. He started his journalism career as an assistant foreign editor at The Washington Post before moving with family to Denver and taking a brief stint with the Denver Business Journal. During a 25-year career at The Post, he covered city and state politics, droughts, entertainment and wrote Sunday takeouts, and was part of two Pulitzer Prize-winning teams for breaking news coverage.

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